Off-road hauling machines are designed to carry large payloads, often up or down steep inclines. Examples of such machines include dump trucks and the like. Such machines are powered by a drivetrain including in many cases, a prime mover or engine, a torque converter, a plurality of wheels or other traction device and a transmission which transmits high torque loads from the prime mover to the wheels under these conditions. Because of the high drivetrain power requirements, a lockup clutch of a torque converter is routinely engaged to minimize power loss. As conditions change, such as a change in grade or an increase in speed, the transmission steps through gear changes to optimize the engine speed to the required torque. Should a gear change in the transmission not progress as expected- and fail to make a clean transition to the new gear, a power surge can ripple through the drivetrain. In the most dramatic cases, this power surge can damage the drivetrain to the point of failure.
U.S. Pat. No. 9,216,741 ('741 patent), issued to the present assignee, is directed to sensing and controlling an engine speed for the purpose of matching crankshaft speed, that is, torque converter input speed, with torque converter output speed during lockup clutch engagement. The '741 patent relies on knowledge of prior and current engine speed when determining lockup clutch engagement and does not to prevent drivetrain damage in the case of a missed shift. It can therefore be seen that a need exists for drivetrain with reduced torque peaks and thus reduced susceptibility to drivetrain damage.